The present invention is directed toward immunochromatographic test strips and more particularly, toward test strips that are color-coded in order to detect the presence or absence of a particular substance in a fluid sample.
The measurement of physiologically important substances in urine, serum, and tissue using immunological principles is well known. In particular, drug-specific antibodies and antigens have been used in a variety of immunological assay procedures for detecting antibodies or antigens in bodily fluids of humans and animals. Test devices are known which can identify the presence or absence of drugs of abuse, such as cocaine, opiates, and marijuana, using the protein conjugates of these drug derivatives and their accompanying antibodies.
U.S. Pat. No. 5,260,194 to Olson discloses an immunoseparating strip for determining the presence of an analyte in a test solution. The test solution contains a fluid sample, an antibody for the analyte, a conjugate of the analyte, and a label. The test device is a bibulous strip which is contacted with the test solution. The bibulous material contains a first receptor capable of binding to the conjugate of the analyte and a second receptor capable of binding to the antibody of the analyte. If the conjugate is present, a signal producing means interacts with the label and produces a signal in relation to the amount of analyte in the fluid sample. This device, however, is a complex system which requires a number of special reagents and test conditions.
U.S. Pat. No. 5,240,735 to Lau discloses a test device which includes a carrier matrix having a reactant system capable of interacting with proteins in a fluid sample to produce a visually detectable and/or measurable response based on changes in pH. The reactant system requires two dyes incorporated into the carrier matrix to provide improved color resolution and increased sensitivity to proteins. The dyes are capable of interacting with proteins and undergo a sufficient and contrasting color transition at approximately the same pH range.
U.S. Pat. No. 5,238,652 to Sun et al discloses an analytical test for assaying various drugs using immunochromatography and colored latex particles which indicate whether the fluid sample contains a particular non-protein antigen being tested. A positive result is indicated by a lack of color. This test, however, may lead to inaccurate results because the location of the reaction is unmarked, therefore, the lack of color in a positive test may be mistaken.